2013 Nov. Research On Periodic Oscillation Test Equipment for Thyristor Valves TBEA Shenyang Transformer Group Co., Ltd. TBEA Energy (India) Pvt Ltd. Reporter: Liu Bufeng

1. Background Introduction With the development of smart grid, more and more power electronic products, such as SVC, HVDC etc., are focused and applied in power system. Thyristor valve is the most important part of these devices, but also the most vulnerable sector. The reliability and stability of valve will influence the products’ prospect applied and promoted in power system. In the real application environment, the safe and reliable turn-on and turn-off of valve is the key during running.

2. Question Provided To ensure PE products meet the stability and reliability requirements during running, some tests need to be done in valve to verify the consistency of cyclic turn-on and turn-off of thyristor valves, to ensure the valve can bear the maximum of voltage, current, thermal intensity etc., and simultaneously, to examine the voltage wave when thyristor valve is triggered uniformly and the voltage wave when BOD works because of triggering inactivation. To verify this, the Periodic Oscillation Test is necessary. Under the limited test conditions, how to do the Periodic Oscillation Test?

3. Purpose of the paper The purpose of this paper provides a simple and practical solution to research the Periodic Oscillation Test Equipment, thus, it can meet the requirements of cyclic triggering and blanking test under the limited test conditions. The paper analyses the security of service to thyristor valve in theory based on the model of valve, and determines the minimum voltage, current, the interval time of triggering between positive and inverse group of valve, etc. And some matters need attention are also mentioned. To make the valve run in actual conditions, the equivalent test should be done which should reflect the actual running condition.

4. Periodic Oscillation Circuit Design (1) Principle (2) Circuit (3) Triggering system The test is to use the charge and discharge of capacitor and reactor to simulate large current flowing thyristor valve.

5. Theory Analysis Parameters calculation: (1)Determine the maximum values of voltage and current Oscillating current bottom width is The wave impedance during discharging is The peak current during discharging is (2) Determine the bottom width of oscillation current If the bottom width is narrow, then the peak current during discharging Im can be transferred large. If the bottom width is wide, then he peak current during discharging Im can be transferred small. (3) Determine the time interval between positive and anti-group It is better to trigger anti-group after the positive group withstands the reverse voltage for 1ms.

6. Application Result (1) Test waveform According to the test circuit, the peak current and the wave impendance can be different by adjusting the L value and C value. The test is mainly to observe the dynamic voltage-sharing during opening and closing. (2) Analysis of test results a. The voltage-sharing during opening process b. Overshoot factor test during shutdown

7. Matters need attention (1)The pulses of triggering positive group and anti-group are got in the negative half-cycle which means the power stops charging. One reason is to avoid accidental short circuit of power, and the other reason is to avoid the test in the charging process so that the measurement error will be caused by uncertain magnitude. (2)After the triggering of postive group, the reverse voltage during shutdown is formed. The triggering of anti-group should avoid the transient peak voltage, so the triggering should be delayed for 0.5ms to 2ms. Thus, positive group and anti-group are both tested, and the reverse voltage after the oscillating current occurred in anti-group is completed can connect the next positive half-cycle energy.

8. Conclusion The above tests show that to use this periodic oscillation test circuit to test valve under limited testing conditions has some advantages. (1)Test circuit consumes little energy, thus simple laboratory can implement it. (2)Energy-saving effect is remarkable. The test has no disturbance to the grid, and it can save space and money, thus has good economic result. (3)Test items and parameters can be easily configured without a lot of changes. The test is more flexible. (4)The test circuit is simple, and the test component also has high security and is not easy to be damaged due to the failure of the test circuit. (5)The valve after testing via the periodic oscillation device generally has no problem in system test.

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